Machine tool and control apparatus of the machine tool

1. A machine tool comprising: a workpiece holding unit to hold a workpiece; a tool rest to hold a cutting tool that cuts the workpiece; a feeding unit comprising a workpiece moving mechanism to move the workpiece held by the workpiece holding unit and a tool rest moving mechanism to move the tool rest to feed the cutting tool toward the workpiece in a predetermined feeding direction by moving the workpiece moving mechanism and/or the tool rest moving mechanism; a vibration unit to cause relative reciprocal vibration between the workpiece holding unit and the tool rest and to make a cutting portion during forward movement of the vibration overlap with a cutting portion during backward movement of the reciprocal vibration; and a rotating unit to cause the cutting tool to rotate with respect to the workpiece or the workpiece to rotate with respect to the cutting tool, the machine tool being capable of cutting the workpiece via the rotation of the workpiece or the cutting tool and via the feeding of the cutting tool toward the workpiece with reciprocal vibration in the feeding direction, wherein the machine tool comprises a vibration frequency setting unit to set vibration frequency of the reciprocal vibration with respect to one rotation of the workpiece or the cutting tool when machining the workpiece based on a difference of heights of concave and convex portions formed on a surface of the workpiece corresponding to paths of the cutting tool during the forward movement and the backward movement and having predetermined heights so that the concave and convex portions are dispersed respectively at different phase positions of the workpiece.

2. The machine tool according to claim 1 , wherein the machine tool comprises an amplitude setting unit to set amplitude of the reciprocal vibration.

3. The machine tool according to claim 1 , wherein the vibration frequency setting unit sets the vibration frequency on the basis of the difference between a maximum value and a minimum value of roughness of a machined surface of the workpiece or on the basis of the maximum value.

4. The machine tool according to claim 3 , wherein the machine tool comprises an amplitude setting unit to set amplitude of the reciprocal vibration.

5. A control apparatus of a machine tool comprising a workpiece holding unit to hold a workpiece; a tool rest to hold a cutting tool that cuts the workpiece; a feeding unit comprising a workpiece moving mechanism to move the workpiece held by the workpiece holding unit and a tool rest moving mechanism to move the tool rest to feed the cutting tool toward the workpiece in a predetermined feeding direction by moving the workpiece moving mechanism and/or the tool rest moving mechanism; a vibration unit to cause relative reciprocal vibration between the workpiece holding unit and the tool rest and to make a cutting portion during forward movement of the vibration overlap with a cutting portion during backward movement of the reciprocal vibration; and a rotating unit to cause the cutting tool to rotate with respect to the workpiece or the workpiece to rotate with respect to the cutting tool, the machine tool being capable of cutting the workpiece via the rotation of the workpiece or the cutting tool and via the feeding of the cutting tool toward the workpiece with the reciprocal vibration in the feeding direction; wherein the control apparatus of the machine tool comprises a control part to control the tool rest moving mechanism and the work moving mechanism and a numeric value setting part to set vibration frequency of the reciprocal vibration with respect to one rotation of the workpiece or the cutting tool when machining the workpiece; and wherein the control part further comprises a vibration frequency setting unit that changes the vibration frequency set by the numeric value setting part based on a difference of heights of concave and convex portions formed on a surface of the workpiece corresponding to paths of the cutting tool during the forward movement and the backward movement and having predetermined heights so that the concave and convex portions are dispersed respectively at different phase positions of the workpiece.